@derek-m Hi Derek - many thanks for this explanation...I think I get it. I would guess in my Daikin setup the heat pump internal unit has the ability to control the flow rate (presumably via the internal unit's pump, indicated in the manual, per pic below - mine is 16kw) and water temps to deliver the delta T which can be set in the controller (I think!). I then have two additional external pumps - one for the UFH, one for the radiators. I have both of these set to '1' (lowest speed of 3). This setup is in line with that recommended for 2 different heat emitters in the Daikin manual (per diagram below, without the fan coil circuit). If the internal unit of the heat pump is altering the flow rate via its internal pump, do you think the external pumps have any effect? Do they modulate the flow rate - i.e., reduce or increase the flow rate according to their setting (1, 2, or 3) to something different to that intended by the brains of the Daikin side of things, or just boost whatever flow rate is determined by the Daikin unit? Or am I misunderstanding everything? If so, apologies.
One thing I've noticed that on the LWT/ RWT dials accompanying the external pumps, the indicated delta T is usually spot on for the UFH (delta t is 5 degrees), but always slightly lower for the radiators (delta t is 2 or 3 degrees). I don't know why that would be - although I've discovered my radiators were never balanced (all lock shield valves are fully open); and the UFH wasn't balanced either (all the blue caps are fully open - I don't have actuators - and the flowmeters fully open), or even labelled with the rooms on manifold pipes. Another odd thing about my UFH manifolds is that the blue caps are on the top row and the red flowmeters on the bottom row, which is the opposite to every photo of an UFH manifold I see here or on the interweb - it works, so not sure that is an issue, maybe just how they do it here in Italy (I should get that on a t-shirt).
As I was trying to make clear in my previous post (though probably not very well), in heat pump system in particular, it is a balancing act between operating the heat pump at the lowest temperatures, whilst supplying the water to the heat emitters at sufficient temperature to meet the heat demand of the building.
When you mention 'the LWT/ RWT dials accompanying the external pumps', are these associated with the 'mixing valves', item 18 on the diagram?
Like many other's, it would appear that your system suffers from having a number of water pumps and a buffer tank (item 11, balancing bottle), which makes controlling the water flow around your system more difficult. In an ideal World, the water flow rate from the heat pump into the top of the buffer tank, would be equal to the water flow rate out of the top of the buffer tank to the heat emitters, but this undoubtedly will not be the case.
I think that in your case, optimum efficiency should be achieved by operating the two external water pumps at the lowest speed setting, to keep the flow rate after the buffer tank as low as possible. If the water flow rate into the buffer tank, is greater than the flow rate going out, then some of the supply water will pass directly through the internals of the buffer tank, and mix with the return water to the heat pump. This will reduce the DeltaT at the heat pump which should then lower the internal water pump speed to restore the desired DeltaT, so the flow rate into the buffer tank should be reduced to approximately match the flow rate coming out.
If the flow rate coming out of the buffer tank is greater than the flow rate going in, then return water from the heat emitters is likely to mix within the buffer tank, and hence reduce the temperature of the water being supplied to the heat emitters. Cooler heat emitters would mean less heat energy into the building, which could mean having to operate the heat pump with a higher LWT to compensate.
Your system would appear to be set to operate in an efficient manner, but a fairly simple check would be to measure the temperature of the water going into the buffer tank and the water coming out of the buffer tank, it these are approximately the same temperature, then your system should be working well.
As far as the lower DeltaT on the radiator supply is concerned, I don't think that you should be too concerned provided that you are achieving the desired indoor temperatures. It merely indicates that the water flow rate through the radiators is greater than that required to meet the heat demand. You could try lowering the LWT produced by the heat pump, which may bring the radiator DeltaT up to the desired 5C, and also improve overall efficiency.
@derek-m As ever thanks for your comprehensive reply...I admit I always have to read your responses several times over due to my limited knowledge and comprehension...I suffer from 'you don't know what you don't know' so sometimes I only get a small part of what you've written; as my knowledge increases due largely to posts on this forum I find that when I go back to earlier responses or other threads, I understand more each time. Heaven knows how your average ASHP customer is meant to cope.
Just to note that I've read other threads on this forum which reference systems where delta T is not a user setting. On my Daikin, I can set the delta T to any value between 5 and 15C (per snapshot from the manual). Hence I was wondering just how the Daikin internal unit does that - presumably via its internal pump and by controlling the water temp (flow and temperature), and what effect the external pumps would have on this - do they interfere or otherwise.
Yes, the LWT/ RWT dials I'm referencing are in the pics attached here - the left is the UFH, and the right the rads. There is a mixing valve you can see in the pic but I independently decided that it was pointless to have it set to mix (its graded min to 5, so I reduced it to min) since with my WCC and the field setting for maximum LWT set to 50, there is no requirement for it (note mine is a HT system and can allegedly produce LW up to 80C). The left dials are LWT & RWT for the UFH; the right dials the same for the radiators. I'm not sure on the buffer tank - I didn't think I had one in my installation - unless its the red tank in the second photo? That is located directly above the additional water pumps in the first picture. If not, I don't have a buffer tank, sorry - its shown on the Daikin diagram but not present (if its not the red tank).
I have both the external pumps set to 1. I've experimented with various settings but it seems to be happy at 1. That said, the flowmeters on the UFH manifolds hardly move at all when I experiment with them fully open or fully closed alongside fully opening or closing the blue manual caps; if I raise the pump to 2, there is more movement, but I perceive it leads to less efficiency/ greater consumption. We also have a recirculation pump fitted for the DHW but that is turned off permanently at the consumer unit. There are no other pumps - I've seen pictures of UFH manifolds for instance with pumps - we don't have these - our pumps are, as in the picture, located close to the Daikin kit.
I spent over 50 years working on complex systems of various types, and found once one learns how equipment has been designed to operate and systems have been designed to function, it eventually starts to fall into place. I am still learning new things about heating systems and the best way they can be operated.
The red cylinder is an expansion vessel, to accommodate the expansion and contraction of the water as it heat up and cools down.
I believe the buffer tank is inside the vertical rectangular insulation to the right of the red cylinder. It appears to have 2 pipes going in on the right-hand side and 2 coming out on the left-hand side, which go to the two circulation pumps.
Whenever there is a difference between the indoor temperature and the outside temperature, heat energy will flow in or out of the building. When the building is losing energy it is necessary to replace the heat energy lost, so as to maintain a constant indoor temperature. The rate at which heat energy is supplied to the building is primarily dependent upon the heating capacity of the heat emitters, the larger the heat emitters, the more heat energy they can provide at a given water temperature. As the warm water flows through the heat emitters, it transfers energy into the building, and in doing so the water cools, such that the return water to the heat pump will be several degrees lower than that supplied.
The rate at which the water is cooled within the heat emitters is dependent upon the supply temperature and the flow rate. If the water is flowing slowly through the heat emitters it will have longer to transfer its heat energy, so the return water will be cooler. If the supply water is warmer, the heat emitters will operate more effectively, which will provide a greater quantity of heat energy into the building. So a higher water supply temperature will provide more heat energy into the building at a constant water flow rate, but this in turn will cause a lower RWT. When this lower RWT reaches the heat pump, it is necessary for the compressor to work harder to put in more heat energy to raise the LWT to the required value.
If the system has been designed to operate with a fixed DeltaT, then to increase the RWT and hence restore the desired DeltaT at the heat pump, it is necessary to increase the water flow rate around the system. Whilst maintaining a constant water supply temperature, increasing the flow rate through the heat emitters will supply approximately the same quantity of heat energy, but the water will not be within the heat emitters for as long a time period, so will not cool to the same extent. The RWT will therefore increase while the LWT remains constant, until the desired DeltaT is once more achieved and the system is balanced.
There are two fundamental things to remember about heating systems.
The amount of heat energy supplied by the heat emitters into the building, is primarily dependent upon the heating capacity of the heat emitters, and the water supply temperature.
The quantity of heat energy provided by a heat pump is a product of the LWT to RWT DeltaT, and the flow rate, though there will be a further aspect to consider if anti-freeze is present in the system.
When the weather is cold, the heat energy demand will be higher. To supply this increased heat energy demand will require a warmer water supply to the heat emitters, which will in turn require the LWT to be increased and the heat pump to work harder. The warmer heat emitters will emit more heat energy, so will extract more energy from the water and cool it more. The cooler return water should cause the water flow rate to be increased to re-balance the DeltaT.
Obviously the above should occur automatically, without user intervention, if the system has been configured and commissioned correctly.
@derek-m Many thanks for taking the time to explain this in more detail - a clear explanation which I'm sure will be useful for anyone reading this thread in the future!
I think the vertical insulated box is the low loss header - see photo. The system in the photo just has the internal Daikin unit, the pumps arrangement with the mixing valve, the expansion tank, a recirculation pump (turned off), the low loss header (if that's what it is) and the thermal store. So I don't think I have a buffer tank - that would be obvious, right? It looks like a small immersion tank? Definitely don't have one of those. Not sure why I don't, although there are configurations in the manual which don't have the balancing bottle (= buffer tank, I assume)...just thought the configuration on p4 was the closest to mine - 2 heat emitters with 1 heat source - although I could be wrong. Manual below for reference as its easier than me trying to describe.
@derek-m Ah, got it - if I google images of a buffer tank it brings up something that looks more like a DHW tank...so the low loss header works like a small buffer tank?
Yes we have three pumps - one on the UFH piping/ circuit set to speed 1 (constant differential pressure setting), one on the radiator piping/ circuit set to speed 1 (proportional differential pressure setting), and one for the DHW which acts as a recirculation pump which is permanently off (zero power) at the consumer unit. Plus of course the pump in the Daikin internal unit. And a big pump on our mains water supply, but that's another story.
@derek-m Ah, got it - if I google images of a buffer tank it brings up something that looks more like a DHW tank...so the low loss header works like a small buffer tank?
Yes we have three pumps - one on the UFH piping/ circuit set to speed 1 (constant differential pressure setting), one on the radiator piping/ circuit set to speed 1 (proportional differential pressure setting), and one for the DHW which acts as a recirculation pump which is permanently off (zero power) at the consumer unit. Plus of course the pump in the Daikin internal unit. And a big pump on our mains water supply, but that's another story.
With your system a water pump for the UFH would always be required to allow mixing to take place to limit the water temperature, but you may not have required the one for CH had a LLH not been installed.
It is not a major problem as long as the water flow rate out of the LLH does not exceed the water flow rate going in, which is being controlled by the heat pump controller. As you appear to be getting sufficient heat energy into your home with both water pumps on speed 1, I cannot see this being a problem.
@derek-m Hi Derek that's good to hear. I have read threads recommending ditching LLH's for efficiency gains. I guess for my system that would involve leaving the pump for the UFH, removing the LLH, removing the CH pump, and connecting the piping back as if the LLH had not been there in the first place. Just to note there is a mixing valve on the UFH circuit but I have it turned down to 'min' as the controller has a setting to limit the LWT and I have this set to 50; its a HT system so notionally I could have been running the LWT at 80 for the rads but don't (anymore).
We do appear to be getting enough heat energy in but I think I need to i) balance the radiators, which at the moment are fully open (TRV's and lockshields); and ii) balance the UFH, which at the moment has all (blue cap) valves and flowmeters fully open; both of these are leading to some perceived uneven heating effects (aided by members of my household leaving the windows open all day for fresh air purposes...).
@derek-m Hi Derek that's good to hear. I have read threads recommending ditching LLH's for efficiency gains. I guess for my system that would involve leaving the pump for the UFH, removing the LLH, removing the CH pump, and connecting the piping back as if the LLH had not been there in the first place. Just to note there is a mixing valve on the UFH circuit but I have it turned down to 'min' as the controller has a setting to limit the LWT and I have this set to 50; its a HT system so notionally I could have been running the LWT at 80 for the rads but don't (anymore).
We do appear to be getting enough heat energy in but I think I need to i) balance the radiators, which at the moment are fully open (TRV's and lockshields); and ii) balance the UFH, which at the moment has all (blue cap) valves and flowmeters fully open; both of these are leading to some perceived uneven heating effects (aided by members of my household leaving the windows open all day for fresh air purposes...).
I can't help much with family member's leaving windows open, other than suggesting that you hand them the next bill to pay. I suppose that you could install window open sensors, and valves to shut off the heating to that area if a window is opened.
I am not an expert on UFH, but I do believe that there are recommendations to limit the water supply temperature to 40C. Whether you require the pump and mixing valve would be dependent upon the highest LWT required to meet the maximum heat demand. Actually, turning the mixing valve to its lowest temperature setting may be counterproductive, since it could be reducing the effectiveness of the UFH loops. The mixing valve should be set to limit the temperature to a maximum 40C, or whatever is recommended for your type of flooring. If the water supply temperature is below this limit then the mixing valve should be closed, with no cooling taking place.
The blue indicators are probably on the solenoids, and indicate whether the valve is either open or closed. The flow regulator is where adjustments to the flow rate should be made.
When it comes to balancing the system, it is probably best to leave all valves fully open in the coldest room, and progressively close in the lockshield valves and UFH flow regulators in each of the other rooms. It can be a lengthy process.
Buffer tanks or LLH's can cause reduced efficiency if the water flow rate coming out is greater than the water flow rate going in. Under such circumstances, some of the return water from the heat emitters, could get mixed with the warmer supply water, and hence have a cooling effect. The water supplied to the heat emitters would therefore be at a lower temperature, which would reduce their effectiveness, requiring a higher LWT from the heat pump to provide the required temperature at the heat emitters. This of course then reduces the efficiency of the heat pump.
@derek-m Hi Derek - understood, thanks for the update - very helpful, as ever. Now I'll confess to something really stupid - our mixing valve near the pumps for the UFH is marked min, 1 through 5, and max - not temperature markings, as it seems many do when I searched on google images. Given I had/ have little knowledge of plumbing, and a little knowledge can be dangerous, I'd assumed that the mixing valve values corresponded to the amount of mixing they would do - some min meant minimum mixing, which I realise now is the opposite of what it actually means, and our mixing valve is essentially like a TRV in terms of the markings. So I thought I was reducing the mixing rather than reducing the maximum temperature down to a minimum. As I'm using weather comp, and the user setting for the max LWT is set to 50, I've opened up the valve to max. The plumber who installed the system had it set to 3 which was possibly right (probably 48 C if my google search is accurate) but I believe opening it up to max won't cause any problems if I don't have LWT higher than 50.
This reminded me of a story I heard a few years ago about financial illiteracy in the UK which reported that many people thought the higher an APR for a credit card, the better was the deal. So put me down for a 'heat pump illiterate' t shirt - I'll even pay for it using a credit card with 200% APR.
@derek-m Hi Derek - understood, thanks for the update - very helpful, as ever. Now I'll confess to something really stupid - our mixing valve near the pumps for the UFH is marked min, 1 through 5, and max - not temperature markings, as it seems many do when I searched on google images. Given I had/ have little knowledge of plumbing, and a little knowledge can be dangerous, I'd assumed that the mixing valve values corresponded to the amount of mixing they would do - some min meant minimum mixing, which I realise now is the opposite of what it actually means, and our mixing valve is essentially like a TRV in terms of the markings. So I thought I was reducing the mixing rather than reducing the maximum temperature down to a minimum. As I'm using weather comp, and the user setting for the max LWT is set to 50, I've opened up the valve to max. The plumber who installed the system had it set to 3 which was possibly right (probably 48 C if my google search is accurate) but I believe opening it up to max won't cause any problems if I don't have LWT higher than 50.
This reminded me of a story I heard a few years ago about financial illiteracy in the UK which reported that many people thought the higher an APR for a credit card, the better was the deal. So put me down for a 'heat pump illiterate' t shirt - I'll even pay for it using a credit card with 200% APR.
Don't apologise for lack of information or knowledge, I am still learning, and revising my thoughts, when it comes to home heating systems. If you can find the nameplate on the mixing valve, you may be able to Google the details to find out what 1 and 5 mean in temperature terms. The temperature limit is to protect the floor from over temperature. If you are now getting more heat energy to your UFH, you may find room temperatures are increasing, so it may be possible to lower the WC curve slightly.
I would suppose that it may be best to adjust the WC curve to provide the desired temperature in the coldest room, with any valves fully open, then use the lockshield valves and UFH flow regulators to achieve the desired temperatures in the other rooms. As the LWT goes up and down with the outside temperature, the room temperatures throughout will hopefully remain reasonably stable.
Hi Derek. I have a further question to this topic if you don’t mind me butting in…
My Daikin (still a mystery to me in many respects) has been running with a low cop around 2 to 2.5 and once it’s reached the target lwt it runs at a low flow rate, 6.5 to 7.1 l/m whereas the manual states the minimum flow rate should be 12l/m.
I can’t set the flow rate, so I have to vary the delta T. Currently the emitter type is set to Radiators which gives a fixed deltaT of 10 degrees. Almost always the difference between ‘inlet water temp’ and ‘leaving water temp’ is between 3 and 5 degrees, which I assume is deltaT according to the system. So my question is Why is this not 10 degrees ?
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